Re: [PATCH v5 07/22] x86/virt/tdx: Implement SEAMCALL function

[Kai Huang]

On Tue, 2022-07-26 at 17:50 -0700, Dave Hansen wrote:
> On 7/26/22 17:34, Kai Huang wrote:
> > > This doesn't seem right to me.  *If* we get a known-bogus
> > > hot-remove event, we need to reject it.  Remember, removal is a
> > > two-step process.
> > If so, we need to reject the (CMR) memory offline.  Or we just BUG()
> > in the ACPI memory removal  callback?
> > 
> > But either way this will requires us to get the CMRs during kernel boot.
> 
> I don't get the link there between CMRs at boot and handling hotplug.
> 
> We don't need to go to extreme measures just to get a message out of the
> kernel that the BIOS is bad.  If we don't have the data to do it
> already, then I don't really see the nee to warn about it.
> 
> Think of a system that has TDX enabled in the BIOS, but is running an
> old kernel.  It will have *ZERO* idea that hotplug doesn't work.  It'll
> run blissfully along.  I don't see any reason that a kernel with TDX
> support, but where TDX is disabled should actively go out and try to be
> better than those old pre-TDX kernels.

Agreed, assuming "where TDX is disabled" you mean TDX isn't usable (i.e. when
TDX module isn't loaded, or won't be initialized at all).

> 
> Further, there's nothing to stop non-CMR memory from being added to a
> system with TDX enabled in the BIOS but where the kernel is not using
> it.  If we actively go out and keep good old DRAM from being added, then
> we unnecessarily addle those systems.
> 

OK.

Then for memory hot-add, perhaps we can just go with the "winner-take-all"
approach you mentioned before?

For memory hot-removal, as I replied previously, looks the kernel cannot reject
the removal if it allows memory offline.  Any suggestion on this?

-- 
Thanks,
-Kai